From: Jan Kara Subject: Re: [PATCH v4 1/5] mm: add mkwrite param to vm_insert_mixed() Date: Mon, 24 Jul 2017 13:15:31 +0200 Message-ID: <20170724111531.GG652@quack2.suse.cz> References: <20170721223956.29485-1-ross.zwisler@linux.intel.com> <20170721223956.29485-2-ross.zwisler@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Ross Zwisler , Andrew Morton , Linux Kernel Mailing List , Jan Kara , linux-doc@vger.kernel.org, David Airlie , Dave Chinner , dri-devel@lists.freedesktop.org, linux-mm , Andreas Dilger , Patrik Jakobsson , Christoph Hellwig , linux-samsung-soc , Joonyoung Shim , "Darrick J. Wong" , Tomi Valkeinen , Kyungmin Park , Krzysztof Kozlowski , Ingo Molnar , ext4 hackers , Matthew Wilcox , linux-arm-msm@vger.kernel.org, Steven Roste To: Dan Williams Return-path: Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-Id: linux-ext4.vger.kernel.org On Sat 22-07-17 09:21:31, Dan Williams wrote: > On Fri, Jul 21, 2017 at 3:39 PM, Ross Zwisler > wrote: > > To be able to use the common 4k zero page in DAX we need to have our PTE > > fault path look more like our PMD fault path where a PTE entry can be > > marked as dirty and writeable as it is first inserted, rather than waiting > > for a follow-up dax_pfn_mkwrite() => finish_mkwrite_fault() call. > > > > Right now we can rely on having a dax_pfn_mkwrite() call because we can > > distinguish between these two cases in do_wp_page(): > > > > case 1: 4k zero page => writable DAX storage > > case 2: read-only DAX storage => writeable DAX storage > > > > This distinction is made by via vm_normal_page(). vm_normal_page() returns > > false for the common 4k zero page, though, just as it does for DAX ptes. > > Instead of special casing the DAX + 4k zero page case, we will simplify our > > DAX PTE page fault sequence so that it matches our DAX PMD sequence, and > > get rid of the dax_pfn_mkwrite() helper. We will instead use > > dax_iomap_fault() to handle write-protection faults. > > > > This means that insert_pfn() needs to follow the lead of insert_pfn_pmd() > > and allow us to pass in a 'mkwrite' flag. If 'mkwrite' is set insert_pfn() > > will do the work that was previously done by wp_page_reuse() as part of the > > dax_pfn_mkwrite() call path. > > > > Signed-off-by: Ross Zwisler > > --- > > drivers/dax/device.c | 2 +- > > drivers/gpu/drm/exynos/exynos_drm_gem.c | 3 ++- > > drivers/gpu/drm/gma500/framebuffer.c | 2 +- > > drivers/gpu/drm/msm/msm_gem.c | 3 ++- > > drivers/gpu/drm/omapdrm/omap_gem.c | 6 ++++-- > > drivers/gpu/drm/ttm/ttm_bo_vm.c | 2 +- > > fs/dax.c | 2 +- > > include/linux/mm.h | 2 +- > > mm/memory.c | 27 +++++++++++++++++++++------ > > 9 files changed, 34 insertions(+), 15 deletions(-) > > > > diff --git a/drivers/dax/device.c b/drivers/dax/device.c > > index e9f3b3e..3973521 100644 > > --- a/drivers/dax/device.c > > +++ b/drivers/dax/device.c > > @@ -273,7 +273,7 @@ static int __dev_dax_pte_fault(struct dev_dax *dev_dax, struct vm_fault *vmf) > > > > pfn = phys_to_pfn_t(phys, dax_region->pfn_flags); > > > > - rc = vm_insert_mixed(vmf->vma, vmf->address, pfn); > > + rc = vm_insert_mixed(vmf->vma, vmf->address, pfn, false); > > Ugh, I generally find bool flags unreadable. They place a tax on > jumping to function definition to recall what true and false mean. If > we want to go this 'add an argument' route can we at least add an enum > like: > > enum { > PTE_MKDIRTY, > PTE_MKCLEAN, > }; > > ...to differentiate the two cases? So how I usually deal with this is that I create e.g.: __vm_insert_mixed() that takes the bool argument, make vm_insert_mixed() pass false, and vm_insert_mixed_mkwrite() pass true. That way there's no code duplication, old call sites can stay unchanged, the naming clearly says what's going on... Honza -- Jan Kara SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org